Cyclonic vacuum cleaners work using cyclonic action to separate out dust and dirt from the dirty air sucked into the cleaner. They generally comprise at least one cyclonic chamber in which the air spins at high speed under the prevailing vacuum pressure, and a respective dirt collection chamber which is arranged to collect the dirt flung out from this fast-spinning airflow. The cyclone chamber and dirt collection chamber are together referred to as a cyclonic stage of separation.
The separation efficiency of a cyclonic stage varies with particle size. Consequently, in order to deal with the range in particles sizes typically found in household dust, a tuned series of cyclonic stages is typically provided. In this sort of multi-stage arrangement, the first stage tends to remove the relatively large particles and then each successive stage is optimized to remove successively smaller particles. The various stages may be packaged together as a single, cyclonic separator, which may be removable from the vacuum cleaner to allow easy emptying of the dirt collection chambers. FIG. 1 shows a typical example of this sort of general arrangement. Here, the vacuum cleaner 1 is an upright vacuum cleaner and a removable multi-stage cyclonic separator 3 is mounted in an upright position on a rolling support assembly 5 forming part of the cleaner 1.
FIG. 2 is a section through the cyclonic separator 3. Here the first cyclonic stage—or ‘primary’—comprises a relatively large, cylindrical bin 7 which acts both as a cyclone chamber and as a dirt-collection chamber. The second cyclonic stage comprises a plurality of smaller, tapered cyclone chambers 9 arranged in parallel (to reduce pressure losses across the secondary stage) which each feed into a second dirt collection chamber 11—the so-called Fine Dust Collector (FDC).
The dirty air enters the bin 7 through a tangential inlet 13 (shown in FIG. 1) to help impart the necessary spin to the airflow inside the bin 7, and the separated dirt collects at the bottom of the bin 7. The air exits the primary through a cylindrical mesh outlet—or ‘shroud’—15 and from here is ducted to the secondary cyclone stage. The air exits the secondary cyclone chambers 9 through the top and is then collected in a manifold 17 and ducted down through the bottom of the cyclonic separator—via a sock filter 19 (for separating very fine particles remaining in the airflow)—to the vac-motor.
The outlet duct 19 and the FDC 11 share a common circular wall, which divides the annular, open end of the FDC 11 from the circular open end of the outlet duct 19. The use of a common dividing wall between the FDC 11 and the outlet duct 19 provides for a compact arrangement.
The base 23 of the cyclonic separator 3 is hinged (the hinge itself is not visible in FIG. 1) to allow the user to empty the contents of the bin 7 and the FDC 11 simultaneously. To ensure an adequate air seal between the base and the walls of the FDC, an annular gasket 25 is provided on the base which compresses against the bottom ends of the inner and outer walls of the FDC 11. Similarly, a flexible, annular lip seal 27 is provided to create a seal between the base 23 and the outer wall of the bin 7.
A drawback has been identified with the scheme shown in FIG. 1. The drawback is that, if the annular gasket 25 between the base 23 and the inner wall 21 of the FDC 11 fails, this then introduces a short circuit between the inside of the FDC 11 and the motor intake—indicated by the dotted arrow in FIG. 1. Consequently, fine dust in the FDC 11 may be drawn in through the motor intake, with the potential risk of damage to the motor.